Spring storms brought more snow to mountains across the Western U.S., bringing water for struggling Lake Powell with them.
The National Weather Service Colorado Basin River Forecast Center on Friday estimated that Lake Powell will receive 5.7 million acre-feet of water between April and July as snow melts off the mountains. An acre-foot is roughly enough water to sustain two houses for a year.
That volume is 89% of the normal runoff for that time period recorded between 1991 and 2020.
Facing extreme drought and climate change since the turn of the century, Lake Powell dropped to a historic low of 22% full in Feb. 2023. The reservoir currently stands at about 32% full.
Three factors determine how much water ends up in Lake Powell: the amount of snowpack on Western mountains, spring temperatures (warmer weather can cause snow to melt faster) and soil moisture (dry soil absorbs melting snow, leaving less water for reservoirs).
Snowpack jumped in March throughout the Upper Colorado River Basin, the portion of the river basin that lies above Lake Powell and includes Colorado, New Mexico, Utah and Wyoming.
On March 1, snow water equivalent — the amount of water contained in snow — above Lake Powell stood at 97% of the median snow water equivalent between 1991 and 2020.
A month later, on April 1, forecasters recorded Upper Basin snowpack at 113% of the median.
(Colorado Basin River Forecast Center) This graph depicts snowpack in the Upper Colorado River Basin, which includes Colorado, Utah, New Mexico and Wyoming. SWE stands for snow water equivalent, which is the measure of how much water is in snow. As of April 1, snow water equivalent in the Upper Basin is 113% of the median snow water equivalent recorded between 1991 and 2020.
Snowpack conditions above Lake Powell improved because of active weather in March, forecasters said, which was the third month in a row with near to above-normal precipitation throughout the Colorado River Basin.
Last month, the Upper Basin saw 130% of average precipitation, bringing precipitation above Lake Powell to 102% of average for October 2023 through March 2024.
But an above-average year for snow doesn’t guarantee an above-average runoff, given the forecast of warm spring temperatures and dry soil conditions.
Right now, forecasters say, soil moisture across the entire Colorado River Basin — which includes Arizona, California and Nevada as the Lower Basin — is close to below normal. Soil moisture is better in the Upper Basin than in the Lower Basin.
When forecasting how much water Lake Powell will get, hydrologists release three possible scenarios. On Friday, forecasters reported that there is a 10% chance that the reservoir could receive as much as 8.3 million acre-feet of water or more from April through July. In a drier scenario, there is a 10% chance that runoff could drop to 4.4 million acre-feet of water or below. The most likely case is that Lake Powell sees about 5.7 million acre-feet of water.
Forecasters in late March predicted that Lake Powell would receive 5.4 million acre-feet of water between April and July.
These estimates guide the management of the Colorado River, which serves 40 million Americans, 30 Native American tribes and sustains various ecosystems and habitats.
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